PSI - Issue 20

Yakovleva S.P. et al. / Procedia Structural Integrity 20 (2019) 190–197

191

Yakovleva S.P. et al. / Structural Integrity Procedia 00 (2019) 000–000

2

1. Introduction One of the most advanced machining technologies is diamond tools processing as pointed by Sudnik et al. (2012), Heinz (1985), Tönshoff et al. (2002). Diamond-metal composites (DMC) for diamond tools are a system consisting of a metal matrix (binder) with diamond grains located in it. Such materials are usually manufactured by powder metallurgy, mainly by pressing followed by sintering. Herewith, high temperatures and the duration of technological processes negatively affect the integrity and strength of diamond as shown by Tönshoff et al. (2002), Hsieh et al. (2000), Cui et al. (2011). Therefore, the development of new technologies that make it possible to manufacture DMC in forced modes for better preservation of the diamond component is relevant. In addition, there is the problem of creating an DMC on binders from fairly cheap and common (compared to hard alloy) powders, in particular iron-carbon alloys by Hsieh et al. (2001). Fundamentally new opportunities for solving these problems are provided by the use of explosion energy. During the explosive compaction of powders in their thin surface layers the temperatures sufficient for sintering are achieved by Krupin et al. (1991), Prummer et al. (2006). If by the time of passage of the unloading wave time to heat transfer deep into the particles, the connection between particles receives a strength exceeding the tensile stresses resulting from the phenomenon of unloading. Herewith, shock waves make it possible to create the thermobaric conditions for elastoplastic deformation of diamond as studied by Pavlovsky (1971), which contributes to better preservation of diamond particles. The method allows to vary widely the compositions of compressible powders and to obtain compacts with the level of properties not provided by traditional sintering methods. In the works by Yakovleva et al. (2001), Makharova et al. (2015) it was shown that the use of additional heat treatment causes the hardening of low-alloy steels treated by an explosion due to the precipitation of fine carbides and the formation of structures with a fine subgrain. This effect can be used to create the DMC with a matrix of iron-carbon alloy powders. As is known, during the operation of composites, the filler bears the main load, and the matrix material serves for transfer of load. In this regard, the resistance of the DMC is primarily determined by the strength of the diamond grains retention in the matrix, that is, both mechanical and chemical adhesion. Crystals of diamond, which are mechanically retained in the matrix, drop out of it when lost to approximately a third of their diameter as shown by Heinz (1985) and Hsieh et al. (2000). Currently, the state of theoretical and experimental research in improving the properties of DMC by creating strong chemical bonds between the matrix and diamond is characterized as a stage of intensive study of various factors that determine the nature and morphology of the products of interaction between them, the patterns of their influence on diamond retention and wear resistance of the composite as shown by Sudnik et al. (2012), Margaritis (2003), Balasubramanian (2014). The level of diamond retention under the influence of operational loads is reflected in the mechanism of wear and removal of diamond grains from the matrix. Thus, the removal of diamond grains by the mechanism offalling out indicates their weaker connection with the binder compared with the cleaving mechanism. Therefore, the study of the mechanisms of diamond component destruction allows us to assess the quality of diamond retention and is important for the development of scientific bases for the synthesis of high-performance DMC. Thus, four main groups of tasks that inevitably arise in the development of diamond-metal powder systems can be distinguished: identification of the formation processes of the structure and properties of the metal matrix; study of the influence of forming technological impacts on diamond particles (their integrity); investigation of the diamond-matrix interface features; analysis of the nature of the composites destruction under operational loads. The purpose of this work is to analyze the effect of explosive compaction and subsequent heat treatment on the main factors determining the wear resistance of diamond composites with a matrix of iron-carbon alloys powders (matrix structure, diamond component preservation, diamond-matrix boundary features, wear mechanism of diamond particles). 2. Materials and methods of experiments An important factor in the effectiveness of DMC is the resistance of the matrix to abrasive wear. It is known that wear-resistant structures should have increased strength, hardness, and also have some plasticity (good wear resistance is provided by high strength, and resistance to the formation and spread of microcracks – by plasticity). To obtain a complex of viscoelastic and plastic properties that ensure the wear resistance of the DMC and the